This invention concerns the use of mesh materials as screens over guttering along the edge of the roof of a house, for the purpose of preventing the entry of unwanted materials such as sticks, leaves, and other tree debris, large insects, litter and the like into the guttering. In some places such guttering is called a gutter or spouting, but the general shape remains the same being a gently sloped open topped channel, usually made of metal or plastics material, positioned to collect rainwater as it runs off a roof.
It is well known that the collection of unwanted materials in guttering causes overflowing of the guttering, blockage of the outflow pipes, constitutes a fire hazard and contributes to corrosion of the guttering. It also contaminates any water collected from the roof for drinking or other domestic purposes.
Many systems are in use, and more have been proposed, which provide a screen of mesh to cover the top of the guttering. Some of these systems require the mesh to be tensioned between rigid fastenings on the roof and the top outer edge of the guttering. The mesh in such systems must be kept somewhat tensioned in order for the leaves and sticks to slide over the edge of the gutter. These are the systems to which the present invention is particularly adapted.
Many attempts have been made to produce a mesh system which successfully excludes foreign matter from guttering. Types of mesh that have been tried include punched metal, expanded (slit) metal, woven wire meshes and fibreglass flyscreen fabric. However in recent years moulded plastic meshes have been the most widely used.
Most of these attempts have resulted in a mesh which is so coarse that much foreign material passes through. Although this material is often small enough to be flushed away without blocking downpipes and drains, it can build up in the guttering and can also contaminate water stored in tanks. Perhaps more importantly though is that such mesh is so coarse that sticks and leaf stems easily become caught in it. Trapped in this way, they protrude up from the mesh thus creating a barrier to the escape of other debris and the mesh thus provides a solid anchor for the build-up of further debris around the guttering area on a roof.
In order to provide a moulded plastic mesh with the combination of sufficient strength and maximum flow area (ie. % of surface through which water may flow), the mesh must be moulded as a relatively thick structure. For some applications it is also desirable to have those strands in the mesh which are aligned in the direction of the length of the guttering protrude out from the general plane of the remainder of the mesh in order to reduce sheeting of water across the mesh during heavy rain.
Water flow through the mesh may be increased if strands in the mesh aligned in the direction of the guttering are formed to extend below the strands at right angles to them. But this introduces a series of contradictory performance requirements. In particular, if the mesh strands aligned longitudinally to the guttering project below the general plane of the mesh in order to facilitate water removal on the underside of the mesh, there is the adverse effect that this increased depth of longitudinal strand increases the longitudinal stiffness of the mesh so that it is difficult to bend along a tight radius during the important tailoring of the mesh to the profile of the roofing material during the installation process. Moulding the mesh from a flexible plastics material would facilitate such bending, but this would be strongly detrimental to the necessary rigidity required for the lateral strands in the mesh which support the span of the mesh between the roof and the outer edge of the guttering. Conventionally a compromise would therefore be required whereby stiffness of the lateral direction would be compromised in order to obtain satisfactory flexibility in the longitudinal direction and flexibility in the longitudinal direction would be compromised in order to achieve sufficient stiffness in the lateral direction.
An object of the present invention is to alleviate the above described disadvantages of the prior art.
Accordingly, in one aspect the present invention provides a screen applied to overlay a guttering on an outside edge of a roof of a building said screen comprising a panel of generally planar mesh affixed along one edge of the panel to the roof and along the opposite edge of the panel to the top outside edge of the guttering, the mesh being formed of moulded plastics material and comprising:                a top face and a bottom face on respective opposite sides of the mesh,        a first array of parallel strands, hereinafter called longitudinal strands, aligned in the direction of said one edge of the panel, and        a second array of parallel strands, hereinafter called lateral strands, integrally moulded with and aligned at right angles to the first array, said first and second arrays of strands defining mesh apertures therebetween extending from said top face to said bottom face,and wherein the lateral strands are made from a stiffer material than that from which the longitudinal strands are made.        
Preferably the lateral strands are made from a stiffer material than the longitudinal strands. Preferably the lateral strands are formed from a material having a greater elastic resilience than the material from which the longitudinal strands are made.
Preferably the lateral strands are at least mostly high density polyethylene and the longitudinal strands are at least mostly low density polyethylene and the mesh is formed using a plastics co-extrusion process. More preferably the lateral strands are high density polyethylene and the longitudinal strands are a blend of from 10% to 20% high density polyethylene with the remainder low density polyethylene.
Some embodiments of the present invention are directed to also alleviating additional disadvantages of the prior art. These will now be discussed.
Some attempts have been made to use a relatively fine mesh for gutter protection and examples are described in U.S. Pat. No. 5,257,482 and Australian patent publication AU-A-38506/93. But such meshes tend to suffer from the problem of too much restriction to the flow of water through the mesh due to surface tension effects. This means that during anything greater than light rain, water tends to flow in a sheeting characteristic along the top surface of such meshes and on over the outside edge of the guttering instead of passing through the mesh into the guttering. Attempts have been made to reduce this sheeting by providing upwardly extending ridges on the mesh parallel to the gutter edge, but such ridges create a significant resistance to the removal of debris on the mesh. Water flow through the mesh may also be restricted by water running along the underside of the mesh; although this eventually runs into the guttering after it hits the top outer edge of the guttering, the presence of that water significantly restricts further flow through the mesh.
It is highly desirable that a mesh readily discards any leaf litter and other foreign material which falls onto or is washed onto it. Non discarded material catches other material and also organically breaks down to drop fine material into the guttering. There is room to improve on the performance of existing meshes in this regard.
Also, it has been found from experimentation that water flow is substantially increased if the holes in the mesh are elongated in the direction of water flow across the mesh, that is in the direction running across the width of the guttering, which is in a direction at right angles to the length of the guttering.
The invention therefore provides that the thickness of the longitudinal strands may extend for substantially the full thickness of the mesh from said top face to said bottom face, the thickness of the lateral strands may extend along their full length from said top face to less than 80% of the thickness of the mesh, the lateral strands may be spaced closer to each other than are the longitudinal strands, and the apertures may have an oval shape with their longer axis parallel to the lateral strands.
Preferably the apertures have a longer axis having a length in the range 4.0 to 5.5 mm and have a shorter axis having a length in the range 2.5 to 3.0 mm. Preferably a flat strip portion lies along said opposite edge of the panel and parallel to the longitudinal strands, said strip portion being substantially flat on its top face which blends gently with said top face of the remainder of the mesh.
The affixation of the mesh to the guttering may be by screws through the flat strip portion, with or without an overlying metal strip. Alternatively the affixation of the mesh to the guttering may be by means of mated strips of a textile hook and loop fastening system adhered to said flat strip portion and to said top outside edge of the guttering.
In another aspect the invention provides a sheet mesh of plastics material for application upon or above roof guttering to prevent the entry of unwanted materials into the guttering, said mesh comprising:                a first face and a second face on respective opposite sides of the mesh, and        a first array of parallel strands aligned in a first direction integrally moulded with a second array of parallel strands aligned substantially at right angles to the first array, said strands defining mesh apertures therebetween,wherein the strands in the second array are made from a stiffer material than that from which the strands in the first array are made.        
The preferred materials for the strands are as described earlier in this specification.
Preferably, the thickness of the strands of the first array extend for substantially the full thickness of the mesh from said first face to said second face and the strands of the second array extend along their full length from said first face to less than 80% of the thickness of the mesh. Preferably the apertures have an oval shape with their longer axis parallel to the lateral strands.
Preferably a flat strip portion lies along an edge of the mesh, said edge extending in the direction of the strands of said first array, said strip portion being substantially flat on said first face which blends gently with said first face of the remainder of the mesh.
Preferably the strands in said second array are spaced closer than the strands of the first array. The apertures through the mesh are preferably of generally elliptical shape which is longitudinally aligned in the direction of the second array.
In a further aspect the invention provides a method of preventing the entry of unwanted materials into a guttering on an outside edge of a roof of a building including affixing a screen over the edge of the roof and the guttering, said screen having a panel of mesh in a generally planar form affixed along one edge of the panel to the roof and along the opposite edge of the panel to the top outside edge of the guttering, the mesh being formed of moulded plastics material and comprising:                a top face and a bottom face on respective opposite sides of the mesh,        a first array of parallel strands aligned in the direction of said one edge of the panel, and        a second array of parallel strands integrally moulded with and aligned at right angles to the first array, said strands defining mesh apertures therebetween,wherein the strands in said second array are made from a stiffer material than that from which the strands in said first array are made.        